Tactics Trainer on Cellphone Issue

I love doing the tactics trainer on my phone whenever I have a small slot of free time in between my classes, however I have noticed an irregular trend.

For some reason, whenever I solve a problem on tactics trainer on my phone I only get around an average of +5 rating per problem, however when I do it on my PC I get about +10 to +15 per problem.

I know some of you will say that I may be taking longer on my phone than my PC, however this is not the case! I have solved some problems in literally 5 seconds and I only get like +8, however when I do them on the PC I get around +12 to +15.

I believe this is simply a coincidence. Each tactic is rated, and if you look at your recent tactics stats, http://www.chess.com/tactics/stats the games where you receive +5 when the problem was solved quickly (100%) it also shows that the problem was slightly easier than previous ones. As when you win against a lower rated opponent, your rating increase will be less than if you won against a stronger opponent.

I know it is based on the performance times of all who complete the tactic, but I find it a bit annoying when I lose points for solving something less fast than others. In a game, I won't get less rating points if I win with 5 mins left on my clock compared to when I have 2 seconds left. Or is that also to prevent programmes from solving it and getting way too high 'surreal' ratings?